Electrical protective system



April 16, 1935. E. M. HUNTER ELECTRICAL PROTECTIVE SYSTEM Filed July 21,1932 iw fi n o r H w W e m a F H @w Patented Apr. 16,1935 Y C I1,998,318

UNITED STATES PATIENT OFFICE I ELECTRICAL PROTECTIVE SYSTEM Eugene M.Hunter, Scotia, N. Y., assignor to General Electric Company, acorporation of New York Application July 21, 1932, Serial No. 623,749

4 Claims. (Cl, 171-312) My invention relates broadly to electricalproand arranged to control suitable signal, or, temtective systems andmore particularly to an autoperature limiting, control cu s. maticsystem for limiting the temperature rise of That a properly calibratedvoltage responsive dynamo-electric machines. device, when connectedacross the field winding 5 It is a well known fact that the life oforganic of a dynamo-electric machine, will be responsive 5 electricalinsulating material decreases rapidly to temperature rise of e achinecan be exwith increases in its average operating temperaplained by thefollowing theory. The temperature. It is therefore important not only tolimit tures of the various windings of a dynamo-electric the maximumoperating temperature of electrical machine are usually about the Same-The l0 machinery but also to keep its average operating De e e rise ofthe field Winding Of a dyhamotemperature as low as possible, Ratings, orguarelectric machine is substantially directly p p antee's, if basedupon a maximum temperature tional to the watts dissipated in thewinding. would often be unsatisfactory because the load- W the requ dWatts hecessaryfie produce a ing, or cooling, requirements to give apredetergiven temperature rise, above a given ambient mined maximummachine temperature will vary temperature, are being dissipated in thefield 15 widely with variations in the ambient temperawinding,thewinding will have'a definite resistture of the machine. Thus, amachinewhich is ance and a definite Current W be flowing adjusted tocarry a predetermined maximum load t oug t. Consequently there W be adefinite without exceeding a given maximum temperature, voltage dropacross the winding. If the resistance will have a high average operatingtemperature of the winding was independent of its tempera- 20 at lowambient temperatures and will greatly exture, changes in ambienttemperature would not ceed the given maximum temperature at highamchange the voltage drop across the field winding. bient temperatures..In order to have atempera- Consequently the watts dissipated in thefield ture rating, or guarantee, which is substantially winding would beconstant thereby causing a conindependent of ambient temperatureconditions, stant temperature rise regardless of the ambient 25 the ideaof basing the temperature rating on the temperature. Actually, theresistance of the field temperature rise of the machine has been widelywinding usually changes slightly with changes in adopted. Thus, amachine is rated not to exceed ambient because changes n a b enObviously a given temperature rise at continuous full load will causechanges i fi d Winding temperature,

operation. Such a rating depends upon the fact for a constant inp to thefield, and most field 30 that it requires substantially the same amountof -windi'ngs have a temperature coefllcient of reheat to produce thesame temperature rise in a sistance which is other than zero. However,the given machine, regardless of the ambient temperchanges in fieldwinding resistance, which tend ature. The rated temperature rise isdetermined to change the voltage drop across the field windbysubtracting the maximum probable ambient ing, are largely compensatedfor by the changes 35 temperature from the maximum allowable maincurrent necessary to have constant watts'dischine temperature. i sipatedin the field winding. Thus, with a field Thus a common rating is an 80temperature winding having a positive temperature coefiicient rise,which is based on a maximum permissible of resistance, a drop in ambienttemperature will 40 temperature. of 120 at a maximum probableamfirstcause a slight decrease in field winding re- 40 bient of 40". lsistance, thereby decreasing the voltage drop In view of the fact thattemperature ratings across the fie d Winding for a given field current,are n generally b d upon temperature e and also decreasing the wattsdissipated. If now there has been a demand for an automatic are Qurrentis increased both the field voltage 5 ngement forv preventing machinetemperature the Watts increase and. Whenthe VOItage rises from exceedinga guaranteed value In is the same as at the higher ambient the wattscordance with my invention I provide an arrange- W111 also be ially thesame. Therefore the ment for this purpose which is particularlyadaptfield temperature W111 Substantially the ed for use in connectionwith dynamo-electric as at h higher p Actually the emperature use willbe slightly higher, for a 50 machines which have fie'ld Win$iingS- Itconsists given field voltage, at the lower ambient because essentlallyOf a Properly callblated Voltage the voltage drop increases as the firstpower of the sponsive circuit controller, or relay, connected fieldcurrent whereas the field watts'increase as across the field winding ofthe dynamo-electric t square of t current machine, whose temperaturerise isto be limited, For most practical purposes the voltage re- 55 beset to hold this rise at the lowest ambient temperature encountered inoperation. The rise which is permitted will then normally decrease withincreases in ambient. Another way would be to compensate the fieldwinding for resistance changes with temperature. For example, if asuitable negative coefficient resistance were connected in series withthe usual copper field winding the overall coefficient could be madezero. A properly calibrated voltage relay would then hold a fixedtemperature rise at all ambients.

At this point it should be stated that the most common cause of machineoverheating is overloading and not the failure of the cooling system. Byoverloading I mean exceeding the volt-ampere rating of the machine. Inthe case of synchronous motors and generators and synchronous condensersthis overloading may occur atrelatively light real power loads. Myinvention only protects machines against the temperature rise producedby overloading and not against temperature rises produced by coolingsystem failures. An object of my invention is to provide a new andimproved protective system for electrical ma chinery.

Another object of my invention is to provide a system for limiting thetemperature rise of electrical machinery. 4

My invention will be better understood from the following description,taken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

Referring now to the drawing, I have shown.

therein an electrical machine I, which is illustrated as a synchronousdynamo-electric machine and which it will be assumed is a synchronouscondenser. Machine I is provided with a field winding 2, which isconnected to be energized by an exciter 3 while the armature of machineI is connected to a power circuit 4. Associated with machine I is anautomatic regulator 5, which need not be of any particular type andwhich is shown by way of example as a voltage regulator of the typedisclosed and claimed in Patent No. 1,848,852, granted March 8, 1932, onan application of Louis W. Thompson and assigned to the assignee of thepresent application. Regulator 5 includes a voltage responsive operatingdevice, such as a torque motor 6, which is connected to the circuit 4,preferably through potentialtransformers I, so as to produce a torquewhich varies in accordance with the voltage of circuit. A suitablerestraining spring 8 acts to bias torque motor 6 so that the motor willbe rotated clockwise, through a given angle, when the voltage exceeds apredetermined value, which is determined by the strength of the spring,while the motor will be rotated counterclockwise if the voltage is belowthe predetermined value. Arranged to be moved by torque motor 6 are slowspeed raise and lower contacts 9 and I], respectively, and high speedraise and lower contacts II and [2, respectively. Contacts 9 and III arearranged to cooperate with a center contact member l3, while the highspeed contacts II and I2 are arranged to cooperate with a center contactmember ll. Center contact members I3 and H are connected throughconductors l5 and IE to the positive side of a suitable control circuitll. Contacts 9 and Ill are arranged to control the operation of a pilotmotor [8 through suitable reversing field windings l9 and 20,respectively. Pilot motor I8 is arranged to operate a variable rheostat2| in the field circuit of exciter 3. Under the control of high speedraise and lower contacts II and I2, are high speed'raise and lowerrelays, or contactors, 22 and 23, respectively. Relay 22 is normallyopen and is arranged to short circuit the entire rheostat 2| when it isactuated. High speed lower relay 23 is normally closed and normallyshortcircuits a resistance 24 connected in the field winding circuit ofexciter 3. When high speed lower relay 23 is actuated it opens itscontacts thereby inserting the resistance 24 in the field circuit.

Connected to be responsive to the voltage of field winding 2, andtherefore to be responsive to the temperature rise of machine I as hasbeen previously explained, is a voltage relay 25. Under the control ofvoltage relay 25 is a time delay relay 26 which may have its actiondelayed in any way and which is illustrated as being provided with adash pot 21 for this purpose. Relay 26 has a set of normally opencontacts 28 which are adapted to complete an energizing circuit for asignal, shown as a bell 29. This energizing circult is from the positiveside of the supply source ll through conductor [6 and signal 29, thecontacts 28 and back to the negative side of the supply sourcethrough aconductor 30. Relay 26 is provided with another set of normally opencontacts 3| which are arranged to complete a circuit for energizingmotor I 8 to operate it, in the proper direction for increasing theresistance value of rheostat 2|, provided this resistance value is belowa predetermined value. This circuit is from conductor l6, throughcontacts 3|, conductor 32, rheostat arm 33, contact 3!, field winding20, armature I 8 and back to the other side of the supply source throughthe conductor 30. Relay 26 is provided with two additional sets ofnormally closed contacts, 35 and 35, which are, connected respectivelyin the circuits controlled by the high speed raise contact II and thelow speed raise contact 9.

In addition to controlling the time delay protective relay 26 inresponse to temperature rise, through the action of the voltageresponsive relay 25, it may. also sometimes be desirable to controlprotective relay 26 in response to overloads on the main machine I andfor this purpou I provide a current relay 3! connected in one of theline conductors of machine I. The normally open contacts of both relays25 and 31 are connected in parallel selectively to close a circuit,including the operating winding of relay 2!, which is connected to thesupply source I! through conductors I5, I6 and 30.

In case it should be desired to control the value of resistance 2|manually, I-provide a simple single pole double throw switch 3|varranged to connect motor it across the supply source l1, selectively,through either one of its field windings I! or 20. I have also showndamping means in the form of an oil pot 33 for damping the action ofthetorque motor 5 and thereby improving the operation of thevoltageregulator. The usual field rheostat II is also shown connected inthe circuit of field winding 2.

The regulator action, which is described in detail .in the aboveidentified Thompson patent, is

briefly as follows: With normal voltage on cir';

of spring 3 and none of the contacts 9, I, II or l2 will be inengagement with their respective center contacts I3 and I4. Resistance2l will also necessarily be of the proper value to produce normalvoltage. Assume now that the voltage of circuit 4 should decrease. Thiswould decrease the electrical torque in torque motor 6 and the spring 8would overcome the torque of the motor and thereby causethe engagementbetween contacts 9 and I3. The following circuit would thereby becompleted: Conductor l6, conductor l5, contact l3, contact 9; normallyclosed contacts 36, field winding l9, motor,l8 an'd conductor 30 to theother side of the supply source. Completion of this circuit would causemotor I8 to operate in such a direction as to cause rheostat arm 33 toshort circuit more and more of resistance 2! thereby increasing thevoltage of exciter 3 and consequently increasing the excitation and thevoltage ofma'chine' I. If the voltage decrease has not been severe thisaction will continue until the voltage is returned to normal, whereuponcontact 9 will leave contact l3 and conditions will be as have beendescribed heretofore. However,

' if the voltage decrease has been severe the difference between theelectrical torque of motor 6 and the mechanical torque of spring 8 willbe so great as to fiex contact 9 thereby causing engagement betweencontacts II and I4. The following circuit will thereby be completed:Conductor l6, conductor. l5, contacts l4 and II, normally closedcontacts 35, the operating winding of relay 22 and back to the otherside of the supply source through conductor 30. "As soon as contactor 22operates the entire resistance, 2|. is short circuited thereby producinga relatively rapid increase in excitation of the exciter andconsequently a relatively rapid increase in excitation and voltage ofthe main machine. In a similar manner, if the voltage of circuit 4should increase above normal relatively slightly the engagement ofcontacts I0 and I3 will cause the energization of motor i8 through thelowering field winding-20 thereby causing a reverse operation of thismotor and an increase in the resistance 21. This decreasesthe excitationof both machines 3 and I and thereby reduces the voltage. A relativelylarge increase in voltage on circuit 4 will cause engagement betweencontacts l2 and I4 through the flexing of contact I 0. This will causeoperation of high speedlowering contactor 33 which acts to insertsuddenly the relatively large resistance 24 in the field circuit ofexciter 3, thereby suddenly decreasing its excitation by a relativelylarge amount, which in turn acts to decrease the excitationandconsequently the voltage of main machine I. v

During the above described operation the instantaneous voltage of fieldwinding 2 may increase considerably above the voltage value cor-.responding to the rated, or guaranteed, temperature rise of machine I:Consequently relay 25 may operate several times, but the time delayfeature of relay 26 is so calibrated that under normal operation of theregulator the duration of these transient high voltages will not besufiicient to cause operation of relay 26. If, however,operatingconditions on circuit 4 should become so extreme as to requireabnormally high excitation, the steady state value of the voltageacross'field winding 2 may reach the predetermined max-' 'imum valuecorresponding the rated temperature rise of the machine. When thishappens, relay 25 closes its contacts thereby completing the energizingcircuit for relay 26, which, in a. predetermined time will operate. Assoon as relay 26 operates, signal 29 will be energized, as haspreviously been described. Similarly, the opening of contacts and 36will effectively prevent the regulator from further increasing theenergization of field winding 2. If the resistance 2| is below a valuecorresponding to full load,'or rated, field current in field winding 2,contact 34 is so adjusted that it will be'in engagement with contact arm33, while as soon as this resistance corresponds to' the value which isequal to or greater than the resistance necessary for producing fullload field current, contacts 34 and 33 will be out of engagement.Consequently, when contacts 3| of relay 26 close, a circuit will be com?pleted through the lowering winding 20 of the motor 18, therebycausingthis motor to operate to increase the resistance-2| in case this resist:ance is of too low a value. This action ivillcontinue until theresistance2l is of the proper value .to produce full load current infield winding 2,

whereupon contacts 34 and 33 will separate thereby stopping motor l8. 7

The time delay feature of relay 26 is also important in preventing theoperation of the protective equipment in cases of transient voltagesinduced in the field winding 2 by transient disturbances on main circuit4. This time delay feature also prevents operation of relay 26 by relay3'! in case of transient overload currents. In case the current incircuit 4 exceeds a predetermined high value for a predetermined lengthof time relay 31 will cause the operation of relay 26 which will theninitiate all of the above described operations.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from my invention, and Itherefore aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope across said fieldwinding and arranged to oper ate at a predetermined maximumfield'voltage, a time delay relay arranged to be operated by theoperation of said field voltage responsive relay, said time delay relayhaving means for preventing said regulator from increasing theenergization of said field winding when said time delay relay operates,said relay having additional means for causing the energization of saidfield winding to be lowered to a predetermined value in case it is abovesaid value when said time delay relay operates.

2. In combination, a dynamo electric machine having a direct currentfield winding, an automatic regulator of an operating condition of saidmachine for varying the energization of said field winding, a relayconnected to respond to the voltage of said field winding and havingcontacts adapted to be closed when thevoltage across said field windingexceeds *a'predetermined value, a relay connected to respond to thecurrent in said machine and having contacts adapted to be closed whensaid current exceeds a predetermined value, a time delayed relayarranged to be operated by the closing of the contacts of either of saidtwo first mentioned relays, a signal arranged to be operated by theoperation of said time delay relay, means for preventing said regulatorfrom increasing the energization of said winding when said time delayedrelay operates, and means for reducing the energization of said fieldwinding to a predetermined value if it is above said value when saidtime delayed relay operates.

3. In combination, an electric machine having organic insulatingmaterial whose maximum permissible temperature rise above any one of anormal range of ambient temperatures as a result of overloading of saidmachine is to be a substantially constant value which is determined byconsiderations of the effect of high temperature upon the deteriorationof said insulation, a variably energized winding on said machine whosewatts dissipated therein is substantially a function of said temperaturerise, and means for limiting the energization of said winding to a valueof watts dissipated therein which corresponds to said predeterminedtemperature rise.

4. In combination, an electric machine having organic insulatingmaterial whose maximum permissible temperature rise above any one of anormal range of ambient temperatures as a result of overloading of saidmachine is to be a substantially constant value which is determined byconsiderations of the efiect of high temperature upon the deteriorationof said insulation, a variably energized winding on said machine whosewatts dissipated therein is substantially a function of said temperaturerise, and means responsive to the energization of said Winding-forindicating when the watts dissipated therein corresponds to saidpredetermined temperature rise.

EUGENE M. HUNTER.

